rados/monthrash: shorten mon pings so that freezing triggers reconnects

This exercises (tho it doesn't necessarily verify) the mon ping reconnect
code when the thrasher freezes the mons.

See #7888.

Signed-off-by: Sage Weil <sage@inktank.com>

suites/rados/monthrash/thrashers/many.yaml

@@ -1,5 +1,13 @@
+overrides:
+  ceph:
+    conf:
+      osd:
+        mon client ping interval: 4
+        mon client ping timeout: 12
 tasks:
 - mon_thrash:
     revive_delay: 20
     thrash_delay: 1
     thrash_many: true
+    freeze_mon_duration: 20
+    freeze_mon_probability: 10